U.S. Pat. No. 4,361,523 dated Nov. 30, 1982 entitled "Humidifier" and U.S. Pat. No. 4,490,311 dated Dec. 25, 1984, entitled "Drum Humidifier" both to Charles G. Shepherd describe a reversible housing for a humidifier of the type to be attached to the ducts of a forced warm air heating system in such a manner that the humidifier can be assembled with the inlet duct positioned to the left or to the right of the humidifier housing, to conform with the particular requirements of an individual installation. In these patents, the housing forms a rigid box with similar side walls and with a top and bottom wall together with a back wall, the box being closed at the front by a cover. One of the side walls supports a drive unit for the humidifier drum while the other side wall has a flanged air passage across which is mounted a drum shaft support bar. To install the housing with the inlet air either to the left or to the right, the housing must accordingly be rotated half a turn about its horizontal axis. The position of the shaft support bar must be inverted.
The humidifier housing is of rigid and relatively bulky construction so that the housing takes space in the truck of a humidifier installer and the humidifier drum shaft supporting bar is a removable piece which might become loose with use, resulting in cylinder drum rattling.